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  <title>设置标记以在保存 PNG 图像时保存完整的 alpha 通道信息（与单一透明色相反）</title>

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</div><hr /><div id="function.imagesavealpha" class="refentry">
 <div class="refnamediv">
  <h1 class="refname">imagesavealpha</h1>
  <p class="verinfo">(PHP 4 &gt;= 4.3.2, PHP 5)</p><p class="refpurpose"><span class="refname">imagesavealpha</span> &mdash; <span class="dc-title">设置标记以在保存 PNG 图像时保存完整的 alpha 通道信息（与单一透明色相反）</span></p>

 </div>
 <div class="refsect1 description" id="refsect1-function.imagesavealpha-description">
  <h3 class="title">说明</h3>
  <div class="methodsynopsis dc-description">
   <span class="type">bool</span> <span class="methodname"><strong>imagesavealpha</strong></span>
    ( <span class="methodparam"><span class="type">resource</span> <code class="parameter">$image</code></span>
   , <span class="methodparam"><span class="type">bool</span> <code class="parameter">$saveflag</code></span>
   )</div>

  <p class="para rdfs-comment">
   <span class="function"><strong>imagesavealpha()</strong></span> 设置标记以在保存
   PNG 图像时保存完整的 alpha 通道信息（与单一透明色相反）。
  </p>
  <p class="para">
   要使用本函数，必须将 alphablending
   清位（<em>imagealphablending($im, false)</em>）。
  </p>
  <p class="para">
   不是所有的浏览器都支持 alpha 通道，如果在你的浏览器上碰到问题，试着用兼容
   alpha 通道的浏览器（例如最新版的 Mozilla）重新加载脚本。
  </p>
 </div>

 <div class="refsect1 parameters" id="refsect1-function.imagesavealpha-parameters">
  <h3 class="title">参数</h3>
  <p class="para">
   <dl>

    <dt>
<em><code class="parameter">image</code></em></dt>

<dd>
<p class="para">由图象创建函数(例如<span class="function"><a href="function.imagecreatetruecolor.html" class="function">imagecreatetruecolor()</a></span>)返回的图象资源。</p></dd>

    
     <dt>
<em><code class="parameter">saveflag</code></em></dt>

     <dd>

      <p class="para">
       是否保存透明（alpha）通道。
       默认 <strong><code>FALSE</code></strong>。 
      </p>
     </dd>

    
   </dl>

  </p>
 </div>

 <div class="refsect1 returnvalues" id="refsect1-function.imagesavealpha-returnvalues">
  <h3 class="title">返回值</h3>
  <p class="para">
   成功时返回 <strong><code>TRUE</code></strong>， 或者在失败时返回 <strong><code>FALSE</code></strong>。
  </p>
 </div>

 <div class="refsect1 examples" id="refsect1-function.imagesavealpha-examples">
  <h3 class="title">范例</h3>
  <p class="para">
   <div class="example" id="example-3190">
    <p><strong>Example #1 <span class="function"><strong>imagesavealpha()</strong></span> 例子</strong></p>
    <div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB">&lt;?php<br /></span><span style="color: #FF8000">//&nbsp;载入带&nbsp;alpha&nbsp;通道的&nbsp;png&nbsp;图像<br /></span><span style="color: #0000BB">$png&nbsp;</span><span style="color: #007700">=&nbsp;</span><span style="color: #0000BB">imagecreatefrompng</span><span style="color: #007700">(</span><span style="color: #DD0000">'./alphachannel_example.png'</span><span style="color: #007700">);<br /><br /></span><span style="color: #FF8000">//&nbsp;做些必须的操作<br /><br />//&nbsp;关闭&nbsp;alpha&nbsp;渲染并设置&nbsp;alpha&nbsp;标志<br /></span><span style="color: #0000BB">imagealphablending</span><span style="color: #007700">(</span><span style="color: #0000BB">$png</span><span style="color: #007700">,&nbsp;</span><span style="color: #0000BB">false</span><span style="color: #007700">);<br /></span><span style="color: #0000BB">imagesavealpha</span><span style="color: #007700">(</span><span style="color: #0000BB">$png</span><span style="color: #007700">,&nbsp;</span><span style="color: #0000BB">true</span><span style="color: #007700">);<br /><br /></span><span style="color: #FF8000">//&nbsp;输出图像到浏览器<br /></span><span style="color: #0000BB">header</span><span style="color: #007700">(</span><span style="color: #DD0000">'Content-Type:&nbsp;image/png'</span><span style="color: #007700">);<br /><br /></span><span style="color: #0000BB">imagepng</span><span style="color: #007700">(</span><span style="color: #0000BB">$png</span><span style="color: #007700">);<br /></span><span style="color: #0000BB">imagedestroy</span><span style="color: #007700">(</span><span style="color: #0000BB">$png</span><span style="color: #007700">);<br /></span><span style="color: #0000BB">?&gt;</span>
</span>
</code></div>
    </div>

   </div>
  </p>
 </div>

 <div class="refsect1 notes" id="refsect1-function.imagesavealpha-notes">
  <h3 class="title">注释</h3>
  <blockquote class="note"><p><strong class="note">Note</strong>: <span class="simpara">此函数需要 GD 2.0.1 或更高版本(推荐 2.0.28 及更高版本)。</span></p></blockquote>
 </div>

 <div class="refsect1 seealso" id="refsect1-function.imagesavealpha-seealso">
  <h3 class="title">参见</h3>
  <p class="para">
   <ul class="simplelist">
    <li class="member"><span class="function"><a href="function.imagealphablending.html" class="function" rel="rdfs-seeAlso">imagealphablending()</a> - 设定图像的混色模式</span></li>
   </ul>
  </p>
 </div>

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